Accelerated statistical image reconstruction methods for X-ray CT X-ray CT provides valuable imaging information for numerous medical applications. Increasing use of CT scans con- tributes signi?cantly to population radiation dose. Decreasing X-ray CT dose will require advances in data acquisition, image reconstruction, post processing, changes in acquisition protocols, and elimination of unneeded scans. Statistical image re- construction (SIR) methods have been used routinely in nuclear medicine imaging for over a decade and have begun to be applied to reduced dose clinical X-ray CT scans. The types of SIR methods that are likely to be most suitable for sub-mSv CT scans use accurate models for the physics and statistics of X-ray CT systems; these methods have required very long computation times that impede their routine clinical use. The primary goal of this project is to develop signi?cantly faster SIR algorithms that will enable routine use of SIR methods for all types of CT scans, particularly sub-mSv scans. The methods developed will be applicable to a wide variety of image acquisition geometries and statistical cost functions, and thus will complement advances in these components by other researchers. Achieving signi?cant acceleration of SIR requires much more than simply waiting for advances in computer technology. Clock frequencies are no longer increasing, and advances in CT technology (e.g., dual energy, dual sources, wider cone angles) continue to increase CT data sizes. Traditional SIR algorithms have been designed mathematically with little con- sideration of modern computing architectures. In this project, imaging scientists and computer scientists will collaborate to develop, implement, and evaluate SIR algorithms that are tailored to modern many-core computing systems that provide parallelism at multiple scales (instruction level, core level, and node level). The goal is to achieve SIR compute times of less than 5 minutes for routine helical chest CT scans at sub-mSv doses, to enable universal use of SIR methods. The methods developed will bene?t all anatomic imaging sites, clinical applications, and patient populations. This project's investigation will focus on a large collection of patient lung nodule CT scans that were acquired at the Univer- sity of Michigan at both 80% and 20% of the usual 40-80 mA (depending on patient size) tube currents for such scans. The 80% dose scans are typically in the 1-1.5 mSv range whereas the 20% dose scans are in the 0.25-0.4 mSv range. The archived sinograms in this collection provide a unique and valuable resource for investigating sub-mSv chest CT and for comparing to regular dose chest CT scans. Both numerical observer studies and radiologist observer studies will evaluate detection performance and morphological characterization of lung nodules with advanced SIR methods at sub-mSv doses. These lung studies are particularly timely in light of the recent USPSTF draft recommendation [1, 2] that is likely to lead to substantial increased use of annual CT exams for patients at risk of lung cancer.